A rapid strep test is used to determine whether a person with a sore throat (pharyngitis) has a group A streptococcal infection.
If the results of the rapid test, which takes 10-20 minutes, are positive, further testing is not needed. If the rapid strep test is negative, a throat culture should be performed on children or adolescents to confirm the results and avoid missing infections that could lead to serious complications, such as rheumatic fever.
A throat culture is more sensitive than the rapid strep test, but it may take 24-48 hours for results. According to 2012 guidelines from the Infectious Diseases Society of America (IDSA), confirmatory testing on adults is not recommended since adults have lower rates of strep throat and far lower risk of complications than children.
When is it ordered?
A doctor will typically order this test when a person has a sore throat and other symptoms that suggest strep throat. There is a higher suspicion of strep when the affected person is a child and/or if the person has been in close contact with someone who has been diagnosed with strep throat.
The Centers for Disease Control and Prevention (CDC) recommends that individuals see a doctor when they have:
- Sore throat lasting more than a week, or recurrent sore throats
- Fever higher than 100.4° F
- Reddened (inflamed) throat with pus (white or yellow spots)
- Difficulty swallowing or breathing
- Hoarseness lasting more than two weeks
- Blood in saliva or mucus
- Excessive drooling in young children
- Symptoms of dehydration, such as excessive thirst, dry mouth, decreased urination
In accordance with the 2012 IDSA guidelines, testing is not recommended when there are also symptoms more closely associated with a viral infection, such as:
- Runny nose
- Mouth sores
Since strep is less common in children under the age of 3, IDSA advises against strep throat testing in this age group unless the child is considered at risk – such as when a family member has been diagnosed with strep throat.
In general, the IDSA advises against the routine screening of asymptomatic people who have been in close contact with someone with a strep throat infection.
What does the test result mean?
A positive rapid strep test indicates the presence of group A streptococci, the bacteria that cause strep throat. A negative rapid test indicates that the affected person probably does not have strep throat, but a throat culture may be performed for confirmation, especially among children and adolescents.
If the throat culture is positive for group A streptococci, then the person tested does have strep throat. In rare cases, pharyngitis may be caused by Group C or Group G streptococci.
These organisms will not cause a positive rapid test but can be detected by culture. If the culture is negative, then it is most likely that the sore throat is due to a viral infection that will resolve on its own.
Is there anything else I should know?
Strep throat spreads from person-to-person through contact with respiratory secretions that contain the streptococcal bacteria. During influenza season, the early symptoms of influenza, such as fever, chills, headache, sore throat, and muscle pain, may mimic strep throat.
To differentiate between strep and influenza, a rapid strep test and a rapid influenza test may be done at the same time.
Most people with streptococcal pharyngitis would eventually recover without antibiotic treatment, but they will be contagious for a longer period of time and are at a greater risk of developing secondary complications.
Strep throat is most common in 5- to 15- year olds. Up to 20% of school children may be “carriers,” persons who have the bacteria but who have no symptoms. Carriers can still spread the infection to others.
Recent antibiotic therapy or gargling with some mouthwashes may affect the rapid strep test results.
How the Test is Performed
The test requires a throat swab. It takes about 7 minutes. The swab is tested to identify group A streptococcus, the cause of strep throat.
How to Prepare for the Test
There is no special preparation. Inform the health care provider if you are taking, or have recently taken, antibiotics.
How the Test will Feel
Your throat will be swabbed in the area of the tonsils. This may make you gag.
Why the Test is Performed
Your health care provider may order this test if you have signs of strep throat, which include:
- No coughing
- Tender and swollen glands in the front of the neck
- White or yellow spots on the tonsils
A negative strep screen most often means Group A streptococcus is not present. It is unlikely that you have strep throat.
If your health care provider still feels that you may have strep throat, a throat culture will be done.
What Abnormal Results Mean
A positive strep screen most often means Group A streptococcus is present, and confirms strep throat.
At times, the test may be positive even if you do not have strep. This is called a false-positive result and is more likely if you have a fever or the symptoms of strep throat.
There are no risks.
This test screens for the group A streptococcus bacteria only and will not detect other causes of sore throat.
One note: The 2012 IDSA guidelines are voluntary and do not represent universal consensus in the medical community on when and how to use the strep test. They reflect current knowledge and expert opinion and are intended to assist in the diagnosis and management of strep throat.